The medical complications of diabetes mellitus are well known. Damage to the small and large blood vessels appears to be associated with chronic hyperglycemia, and as a consequence, diabetic individuals in poor metabolic control have a greatly increased risk of developing retinopathy, nephropathy, peripheral neuropathy, and serious cardiosvascular disease. One organ generally ignored in discussions of diabetes-related complications is the brain, yet an increasing number of reports have suggested that at least some diabetic individuals show significant impairments on a wide range of cognitive tests. Our own work with adolescents suggests that while degree of recent metabolic control is not obviously related to neuropsychological functioning, the age at onset of diabetes is a powerful predictor of impairment. What happens as diabetic individuals reach adulthood and begin to manifest medical complications of diabetes? Will they also show evidence of neurobehavioral deterioration? To date, there has been no systematic assessment of adults with Type I (insulin- dependent) diabetes. Although several investigators have suggested that poor metabolic control may be associated with a reduction in mental efficiency, those studies have been based on relatively limited assessments of small numbers of subjects. No attempt has yet been made to examine the complex inter- relationships among diabetes-related variables and organismic variables (e.g., age; gender). The proposed study will examine these relationships in a large, randomly selected sample of adults who were treated for Type I diabetes at Children's Hospital of Pittsburgh between 1950 and 1979. A nondiabetic comparison group will also be recruited. Three types of behavioral measures will be used: formal neuropsychological tests; information-processing tasks; psychosocial assessment questionnaires. In addition, detailed biomedical data on diabetes-related variables will be obtained since all diabetic subjects are concurrently participating in the Epidemiology of Diabetes study. As a consequence, each diabetic patient will have recently received a complete physical examination and specialized tests assessing medical complications. Our ultimate goal is to determine the relationship between neurobehavioral functioning and the severity and extent of micro-and macrovascular complications.